Molecular dynamics investigation on the interfacial shear creep between carbon fiber and epoxy matrix

Carbon fiber reinforced polymer (CFRP) composite is subject to external loads during service life, suffering interfacial creep between fiber and matrix and eventually interfacial slippage. The interfacial creep degrades interfacial integrity of composites and weakens long-term durability. In order to understand the degradation, microscopic details of interfacial structural changes during creep are essential. This study aims to investigate microscopic creep behavior of carbon fiber/epoxy interface at different shear load levels using molecular dynamics simulations. A molecular interface model consisting of epoxy molecule bonded to graphite sheets representing fiber outer layer is constructed, which is validated by comparing mass density, glass-transition temperature and Young’s modulus of bonded epoxy with experimental measurements. According to creep simulation, there is a threshold stress for the onset of creep failure, above which the interface detaches. Comparatively, no interfacial detachment occurs in low stress regime, where displacement–force curve is plotted and used to quantify energy barrier to the onset of creep failure. Meanwhile, strain and stress evolution of the interface are correlated to interfacial structural changes to understand interfacial creep mechanism. This study provides molecular insights into interfacial creep behavior in fiber-matrix system and form the basis of multiscale investigation framework on interfacial creep behavior